Su Carby Help

[KE70PWR]

hi i have just put twin su's on my 4k and having problems

i seem to be able to get it to start with the choke thats all fine, but when i go to give it some gas even if i let it warm up heaps it seems to bog, then as i let it off it revs up a lil then back again. I have very limited knowledge of the su's but have been trying to read everything i can i seem to have done it all right but it still happens can anyone help me at all or any idea's

[altezzaclub]

Ok- under the edge on each one should be a little moveable piston that lifts the main piston up inside the chamber. That alters the airflow over the venturi throat and hence changes the mixture.

 

With it idling you lift one piston a few mm and feel for when it start to life the main piston. There should be a noticeable bit of added weight when it starts to lift it. You could look down the throat and see. Then lift the main piston a few mm and see what the revs do. If it is too lean, it will die. If it is about right it will speed up a little, then die if you lift it any more. if it is too rich it will speed up all the way through. You check each carb and adjust the idle mixture as needed. Once idle mix is set, you are relying on the needle taper to run the motor over all its revs. You can make a needle richer by sanding it away easily enough, its what I did with mine.

 

After that, the oil is next. When you boot it suddnely, the oil in the dashpot stops the piston leaping up and letting too much air in at reduced suction. The oil holds the piston down over the venturi floor and the extra suction richens the mixture for acceleration momentarily. Thicker oil makes it richer, thinner oil makes it leaner. Try anything from SAE 50 down to 10, & although automatic gearbox ATF is most common plenty of people use engine oil.

 

The springs inside the carb top hat hold the piston down and so keep it richer after the piston lets it up. You can get three different springs, or take them out and see how it goes. I think they have more of an effect at high engine revs.

 

See if there's anything helpful in here, or PM me with questions. Mine are running superbly!

 

http://www.rollaclub.com/board/topic/42407-the-girls-ke70/

[snot35]

And naturally, make sure everything moves smoothly. The pistons should be able to be lifted and drop smoothly and completely. Also make sure your ignition system is spot on.

[KE70PWR]

Thanks guys all sorted not I think should have her back on the road in a week or so that will be the test